Level is a Character Stat in The World Ends With You.
The concept of Level (Lv.) in The World Ends with You works a bit differently from other games. Although a "Level-Up" message will appear in battle once characters have received enough Experience Points, there is no set Level and the Player is free to change their current Level before a battle starts and up to the Maximum Level.
When you level up in battle, your HP Gauge is completely refilled and nearby enemies are damaged.
There are actually two types of Level: Your current level being used and your maximum level, the highest one you can use. To change the level you are currently using, there is a slider on the Phone Menu. As you move it to the left and decrease your level, your Max HP drops by 50 per level in exchange for 1 point of Drop Rate, and vice-versa.
Additionally, the Noise Report on the Phone Menu records will show the lowest level you have managed to beat each particular enemy at on difficulties Normal or higher. It is also possible to increase your maximum drop rate level through food items such as curious mushrooms and absolute shadow ramen. By consuming these items, your maximum drop rate level increases.
The highest level you can achieve is "Star" (Lv. 100). Once you reach Level 99, you will notice that there is one more level to go. (Indicated by the non-zero number of EXP needed after the “NEXT” label) After you gain enough EXP, you will reach the “Star” Level and you'll no longer need to Level-Up anymore, you've reached the maximum Level. Your Level will be displayed as [Your current Level]/Star.